Electrically heated screen construction and method



y ,1965 1'.w. HANNON 3,195,725

ELECTRICALLY HEATED SCREEN CONSTRUCTION AND METHOD Filed Aug. 2. 1961' sSheets-Sheet 1 INVENTOR. Thomas W Hwzzzwn ATTORNEYS July 20, 1965 1-. w.HANNON ELEGTRICALLY HEATED 501mm CONSTRUCTION AND METHOD Filed Aug. 2,1961 3 Sheets-Sheet 2 ATTORNEYS July 20, 1965 T. w. HANNON ELECTRICALLYHEATED SCREEN CONSTRUCTION AND METHOD Filed Aug. 2, 1961 3 Sheets-Sheet5 UK I.- 27

\ mmvroze. mom WHwzuwn BY ATTORNEYS United States Patent 0 3,195,725ELECTRICALLY HEATED SQREEN CGNSTRUCTZSN AND METHGD Thomas W. Hannah,Canton, Ghio, assignor to F. R. talisman & Sons, Inc, Canton, Qhio, acorporation of Filed Aug. 2, 1961, Ser. No. 128,866 14- Claims. (6!.299-238) My invention relates to improvements in electrically heatedscreen construction, and the method of supplying electrical energy toscreens to be heated. Even more specifically, my invention relates to anew and novel transformer construction and the means for electricallyconnecting the same with units which have limited movement relative tothe transformer during operating and use thereof, such as vibratingelectrically heated screens.

Various forms of equipment have been provided for the industrialscreening of materials, such as iron ore and other similar types ofmaterials. Most of such equipment has included a platform supporting oneor more generally horizontally positioned and usually sloping screenswhich are vibrated in some manner in order to accomplish the screeningoperation.

Although various attempts have been made to produce vibratory movementof the screen without greatly affecting the supporting frame membersthereof, the most practical and satisfactory method is to vibratevirtually the entire screening unit including not only the screens, butalso the supporting frame members thereof. This has usually beenaccomplished by providing a resilient mounting for the supporting framemembers on a supporting surface in such a manner as to retain thesesupporting members in place, and then provide some form of vibratingmeans which vibrates the supporting frame members and screens relativeto these resilient mountings.

it has also been found that not only is vibration of the screens throughwhich the material must pass required, but heating the screens is somemanner during the screening operations will add greatly to thefunctioning thereof, by causing less blinding or clogging of the screensduring this operation. The simplest manner of accomplishing this heatingof the screens is to provide the screen cloth which forms the screens ofan electrically conducting material and passing a low voltage electricalcurrent therethrough. In this manner, the screen cloth itself provides aresistance heating unit to supply the necessary heat.

Many problems have been involved in the provision of these electricallyheating and vibrating screen unts, certain of which have involved theproblem of just exactly how to provide an electrical connection to thescreen cloth for properly passing the electrical energy therethroughwhile still maintaining the screen cloth properly tcnsioned to supportand vibrate the material being screened. Furthermore the screen clothmust be easily removable and replaceable in view of the relatively shortuseful life of the screen cloth under the usual abuse and wearencountered.

These electrical connection, support and replacement problems have beenextensively solved according to the principles and constructions setforth in my prior Patents Nos. 2,704,155 and 2,812,062, both entitledElectrically Heated Screen Construction, and dated March 15, 1955, andNovember 5, 1957, respectively.

One of the major problems still remaining in electrically heated screenconstructions, which problem is also encountered in various other typesof electrical installations where it is necessary to supply electricalenergy to a unit which has a limited movement or vibratory movementduring the operation thereof, is how to supply this electrical energy tothe vibrating or moving unit from a stationary source and still maintainthe necessary electrical ice connections intact despite the relativemovement between the source and the unit being supplied. Prior to thepresent invention, the attempts to accomplish this have been through theuse of various forms of flexible electrical cables which have usuallybeen connected to the secondary of a transformer and to the moving orvibrating unit so as to attempt to provide the flexibility for therelative movement therebetween.

For instance, in screen heating constructions, the screen cloth servingas the screening medium has been connected to the vibrating frame of thescreen heating unit through generally hook-shaped, selectivelyadjustable skirt boards, which are mounted on and adjustable withrespect to side rails or frame members. These skirt boards are providedwith electrical conducting means contacting and supporting the sideedges of the screen, and flexible electrical cables, usually in the formof braided copper cables, have been connected to the conducting meansand to a usual transformer mounted in a stationary location adjacent thevibrating screen unit.

These flexible electrical cables have served the purpose of providingfor relative movement between the stationary transformer and the movingor vibrating screen unit, but such cables are relatively expensive andare serviceable for only a relatively short period of time, therebyrequiring frequent replacement and further adding to the expense thereofthrough the additional maintenance costs and lost production time foruse of a particular unit. For these reasons, it is desirable to providesome means of supplying electrical energy from a transformer unit to aunit required to have limited movement for operation thereof, such asvibrating screen heating units, which eliminates the high expense andfrequent maintenance of the usual flexible electrical cables.

It is therefore a primary object of the present invention to provide anelectrically heated screen construction and method which solves theforegoing problems, the principles of which are applicable not only tovibrating screen heating units, but which are also applicable toconstructions Where electrical energy must be supplied from a stationarysource to a unit which must have limited movement for the operationthereof.

It is a further object of the present invention to provide anelectrically heated screen construction having a unique form oftransformer which is connected to the vibrating screen unit preferablysolely by air, yet will properly supply the electrical energy for and tothe vibrating screen to be heated.

it is still a further object of the present invention to provide anelectrically heated screen construction in which the secondary of thetransformer supplying the necessary electrical energy is connected tothe transformer primary preferably solely by air, so that thetransformer secondary may be secured to the vibrating screen unit andfreely vibrate therewith, while the transformer primary may be mountedstationary, thereby solving the problem of a flexible connection betweenthe transformer and vibrating screen unit.

It is an additional object of the present invention to provide anelectrically heated screen construction in which the transformer primaryis mounted stationary and connected preferably solely by air to atransformer secondary secured for free vibration with the screensupporting and tensioning skirt boards of a vibrating screen unit, yetthe transformer secondary is connected to the skirt boards forpermitting selective adjustment of the skirt boards relative to thetransformer secondary, thereby permitting selective adjustment of theskirt boards to tension and properly support the screen clothaccomplishing the screening function.

Finally, it is an object of the present invention to provide anelectrically heated screen construction and method which satisfies theforegoing objects in a simple iprinciples -are set forth in thefollowing description and illustrated in the'accompanying drawings, andwhich are particularly and distinctly pointed out and set forth in theappended claims forming apart hereof.

The general principle involvedin' theelectrically heated screenconstruction of the present invention may be broadly stated forapplication to electrical units generally as including" a transformerprimary assembly formed with an opening extending longitudinallytherethrough and with said primary assemblybeing adapted for stationarymounting. Further, the unit'may include an electrical power consumingunit having electrical connectors thereon and a closed electricalcircuit therethrough between said connectors, with this electrical powerconsuming unit being mounted for movement within predetermined limits,such as vibrating. Still further, the unit includes transformersecondary means havin'g'ends connected secured to the electricalconnectors of the electrical power consuming unit for movement of thesecondary means with the electrical power consuming unit and with thesecondary means extending through the primary assembly opening. Finally,the transformer secondary means, in

its, extension through the primary assembly is mounted free ofanyconnection with the primary assembly which would restrict free movementof the secondarymeans longitudinally through and laterally Within theprimary assembly opening.

The method involved in the electrically heated screen construction ofthe present'invention as applied to electrical units generallymay bebroadly stated as the method of supplying electrical energy to anelectrical power consuming unit which is mounted and adapted. forlimited movement and which is provided with electrical connectors and aclosed electrical circuit between said connectors. Such method broadlystated includes the steps of providing a transformer primary andpositioning a transformer secondary extending longitudinally through theprimary while maintaining the secondary free of connection with theprimary which would restrict freelongitudina l movement of the secondaryrelative to the primary andifree lateral movement of the secondarywithin thejprimary. Still further the method broadly includes the stepof'maintaining the secondary secured to the electrical connectors of theelectrical power consuming unit to form a closed secondaryelectricalcircuit through the secondary and through the electrical powerconsuming unit while the secondary is rigidly maintained movable withthe electrical power consuming unit.

As applied more specifically to electrically heated screenconstructions, the invention may be stated as includinga screensupporting frame member having vibrating means operab lyfconnected,thereto for vibrating. the framem nbe ith a s r en a r e n ns-d m t eframe member. Further, the construction inclndes electricalconnectorsoperably connected to the screen forming ajclosedelectricalcircuit through the screen and between said connectors.

Still further, the construction includes a transformer primary havingancpening formed longitudinally therethroug'h. and a'transformersecondary mounted extend-1 ing longitudinally through the primaryopening and being securedytothe screen electrical connectcrs forvibrating movement with the screen and screen frame. Finally; thetransforrner secondary is mounted free of connection with the primarywhich would restrict longitudinal movement of the secondary throughtheprimary opening and lateral movement of the secondary within the primaryopening.

By way of example, embodiments of the improved electrically heatedscreen construction and method of the present invention are illustratedin the accompanying drawings forming a part hereof, wherein likenumerals indicate similar parts throughout thetseveral views and inwhich: 7

FIG. '1 is. a perspective view showing an electrically heated screenunit constructed according to the principles of the present invention;

FIG. 2, an enlarged fragmentary end elevation of one 7 of thetransformers constructed according to the principles of the present,invention showing the operable connection thereof to the screensupporting unit and looking in the direction of the arrows 22 in FIG. 1;

FIG. 3, a reduced fragmentary top plan view of the transformer of FIG.2; i a

FIG. 4,' an enlarged fragmentary sectional view, part in elevation,looking in the direction of the arrows 4-4 in FIG. 3; V

FIG. 5, an enlarged horizontal sectional view of the transformer primarywith a portion of the secondary being shown extending therethrough inoperable position;

FIG. 6, a fragmentary side elevation, with parts broken away, of thetransformer primary and looking in the directionof the arrows 6,6 inFIG. 5;

FIG. 7, a fragmentary top plan view, with parts broken away showing thetransformer primary with a second embodiment of a portion of a'transformer secondary extending therethrough.

Referring to the drawings, an electrically heated screen constructionaccording to. theprinciples of the present invention is shown in FIG. 1and includes a vibrating screen unit, generally indicated at 10,transformer primaries, generally indicated at 11, and transformersecondaries, generally indicated at 12. The unit illustrated includestwo transformer primary and secondary assemblies, but these assembliesare substantially identical so that only one need be considered for anunderstanding of the principles, of the same.

The vibrating screen unit 10 is basically of a standard constructionwith certain'changes for adaptation of the same to the principles of thepresent invention, and includes a screen supporting frame, generallyindicated at 13, which is mounted on a supporting surface for vibrationrelative thereto by the resilient mounting members 14. The screen unit10 is vibrated, including the total screen supporting frame 13, by astandard vibrating unit, generally indicated at 15, andagain being ofusual construction inrunits of this. type. V Y

Further, the screensupportingframe 13is provided with the spaced andopposed side rails- 16, which side rails iii-turn support the usualselectively adjustable generally hook-shaped skirt boards 17. The skirtboardsi l7 in turn engage and tension and support the screen. cloths 18which perform the screening, function of the unit.

The details, of the constrnctionfof the skirt boards: 17 are set forthin my before mentioned Patent No. 2,812,062 and are, therefore,considered only briefly here.

7 Each skirt board 17 includes a supporting web portionylQ having anupper end 20 pivotally abutting the particular side rail 16 and a lowerend 21, uponwhich'is mounted a generally hook-shaped bus bar ZZ. i i 1 VThe side edges of the screen cloth lsrpositioned at the skirt board 17are formed with hook-shaped edge portions 23 which are reversely engagedwith the skirt board bus bars 22. Thus, when the skirt boards '17 arepivotally adjusted relative to the side rails 16 by manipulation of thetensioning bolts 24; the screen cloths 18,v may be tensioned andsupported between the opposed skirt boards 17 in p roper screeningposition. V

In the particular unit illustrated'iri FIG. 1, there are four separatedscreen cloths 18 which are positioned'for forming the closed electricalcircuits from the skirt board 17 adjacent one of the sides of atransformer secondary 12, through the particular screen cloth 1%, to theopposed skirt board 17, Within the skirt board to the next adjacentscreen cloth l8, and back to the skirt board adjacent the other side ofthe same transformer secondary 12. With this construction, therefore,the bus bar 22 of the skirt board 17 adjacent the transformer secondary12 is formed divided between each screen cloth 18, whereas the bus bar22 on the opposite skirt board 17 is continuous for each set of screencloths 1S and divided only between the sets.

The bus bars 22 are insulated from the respective skirt boards 17 andare connected to the particular transformer secondary 12 by thegenerally L-shaped, preferably copper, electrical connectors 25. Inorder to provide the electrical circuit through the bus bars 22 andscreen cloths 13, these bars and cloths also must be electricallyconducting materials, with the bus bars preferably being copper and thescreen cloths being formed of a selected electrical conducting materialdepending on the particular material to be screened, that is, thevarious abrasion and other factors to be considered for providing amaximum operable life.

Each transformer secondary 12 is generally U-shaped and is formed by apair of generally laterally extending side members 26 connected at theirends, spaced from the particular side rail 155, by a generallylongitudinally extending connecting member 27. In the particularembodiment shown, the secondary side member 26 and connecting members 27are preferably hollow and of generally rectangular crosssection and inthis case the transformer secondaries 12 would be adapted for highcapacity requirements.

Furthermore, as best seen in FIGS. 3, 4 and 5, the con necting members27 of these transformer secondaries 12 may also be provided with aseries of spaced holes 23 formed therethrough and opening into thehollow interiors of the connecting members, which will even more greatlyincrease the capacity thereof by providing air circulation forminimizing the temperature build-up therein and thereby minimizing thevoltage loss in the secondary 12 which would be caused by suchtemperature build-ups. In the case Where capacity is not a prob lem andlow capacity i sufficicnt, the secondary side and connecting members 26and 27 may be formed solid and in every case must be formed of anelectrical conducting material, preferably copper or aluminum.

The transformer secondaries 12 are supported on the screen supportingframe 13 by the generally L-shaped shaped support brackets 29, which aresecured to the particular side rail 16 and preferably mount thesecondary side members as in generally horizontally extending positionsthrough the fastening bolts 30. Bolts 30 are insulated from the supportbrackets 2d by the insulating washers 31 and furthermore, the sidemembers 26 are also insulated from the support brackets 29, preferablyby the insulating sheets 32 positioned thercbetween and formed of aninsulating material such as fiber-glass or the like.

A selectively adjustable secondary connector, generally indicated at 33,is provided between each secondary side member 26 and its respectiveelectrical connector 25. These secondary connectors 33 are formed by theslotted, generally T-shapcd plates 34 and the fiat plates 35, as bestseen in FIGS. 2, 3 and 4.

The slot-ted plates 34 are provided with the flat, generallyhorizontally extending side fianges 36 which are bolted flatwise on theelectrical connectors 25 and these flanges 36 are connected to aupstanding generally laterally extending portion 37 which has a slot 38opening toward the particular secondary side member 2%. The fiat platesare mounted in pairs secured to the secondary side members 26 in spaceupstanding positions for receiving the slotted plates 34 therebetween,and these fiat plates 35 are selectively releasably secured to theslotted plates 34 by a selectively releasable fastening bolt 39*.

Thus, the transformer secondaries 12 are mounted secured on side rail 16by the support brackets 2? and will vibrate with the remainder of thescreen supporting unit, but in order for the skirt boards 17 to beselectively pivotally adjusted with respect to the side rails 16 inorder to properly tension the screen cloths 18, these selectivelyreleasable secondary connectors 33 are provided. When the skirt boardsl7 have been properly adjusted, the fastening bolts 39 of thesesecondary connectors 33 are tightened to provided a positive electricalconnection from the transformer secondaries 12 through these connectors33 and through the electrical connectors 25 into the screen cloths 18.In view of the fact that these econdary connectors 33 form an importantpart of the transformer secondary circuit, they are also formed of anelectrical conducting material, preferably copper or aluminum.

The transformer primaries ll are formed preferably generally cylindricaland are provided with preferably generally cylindrical andlongitudinally extending openings 49 therethrough. Furthermore, eachtransfori ier primary ll may be mounted on a stationary supportingsurface 41 in usual manner and may be provided with the usual sealedcontrol portion 42 having the selectively movable control knob 43.

The main portion of each transformer primary ll is formed by a hollow,generally cylindrical, preferably steel core which may be formed annularshape merely by tightly wrapping strip steel, as shown, to the desiredsize. This annular core dd is then transversely Wrapped preferabiycompletely around the circular extent thereof by a wire coil 45, whichwire coil is separated from core 44 by the usual insulating means 46.

A second wire coil 47 may be wrapped in a similar manner about the firstcoil 45 and likewise separated therefrom by the usual insulating means43. Finally, the outer coil 47 is covered completely with furtherinsulating means d? and the entire unit is completely enclosed in apreferably stainless steel case or enclosure 5%, so that the case $9,which is completely insulated from the remainder of the transformerprimary 11, forms the exposed hollow generally cylindrical shell.

As shown, the connecting member 27 of the particular transformersecondary 12 is supported extending longitudinally through theparticular primary opening it) and is preferably maintained spacedlaterally from the case 5t) so that none of the vibratory movement ofthe secondary 12; is imparted to the primary 11. Thus, the onlyconnection between the transformer primaries 11 and sec ondaries 32 isan air connection and absolutely no wear can take place between theseprimaries and secondaries. Furthermore, since the secondaries arerigidly secured to the vibrating screen unit 1% for vibration therewith,virtually all possibility of wear is eliminated.

As illustrated in a second embodiment in FIG. 7, in the case Where theparticular application permits, the connecting member 27 of thetransformer secondary 12 may be a braided cable 51 of copper oraluminum. In this case, the cable 51 may either be supported spacedtotally from the transformer primary Ill and extending through theopening it) thereof, or where conditions permit and limited wear can betolerated, this cable may lay on the case S6) of the primary andextending through the opening.

In view of the fact that case Ell is completely insulated from theelectrically conducting portions of the transformer primary it, theconstruction will still operate satisfactorily even thoughthe cable islaying on the case. There is in this case, however, going to be limitedwear of the cable 51 due to the vibratory motion thereof relative tocase 59, but in certain cases, this can be tolerated and it would not beof a magnitude to present the problems of a flexible cable soured to astationary transformer and secured to a vibrating screen unit.

In use of the first embodiment construction of the present invention,the screen cloths 18 formed of electrically conducting material areproperly positioned with the edge portions 23 thereof engaged with thebus bars 22 of the skirt boards 17, andfor this purpose, these skirtboards may be pivoted away from the respective side rails 16 byloosening the tensioning bolts 24. In order to permit this pivotalmovement of the skirt board relative to the side rail 16, however, wherethe bus bars 22 are connected to the electrical connectors of thetransformer secondaries 12, it is necessary to also loosen the fasteningbolts 39 of the secondary connectors 33, permitting relative movementbetween the T-shaped slotted plates 34 and their respective connectingplates 35.

After the cloths 18 have been engaged by the skirt board 17, thetensioning bolts are tightened to properly tension the screen cloths forperforming the supporting and screening functions thereof. Once thesescreen cloths 18 are properly tensioned, the fastening bolts 39 of thetransformer secondaries 12 may be tightened to provide virtually a solidconnection between plates 34 and of the secondary connectors 33 and,therefore, virtually a rigid or solid connection between the electricalconnectors 2S and the secondary side and connecting members 26 and 27.

Again, in the preferred embodiment shown in FIGS. 1 through 6, with thetransformer secondaries 12 formed by the rigid side members 26 andconnecting members 27, and with side members 26 rigidly supported on theside rails 16 of the screen supporting frame 13, the connecting members26 will be positioned extending through the longitudinal openings of thetransformer primaries 11 spaced laterally from all portions of theprimary case Stl. Thus, when the vibrating unit 15 of the screensupporting frame 13 is operated to vibrate the entire screen supportingframe, these vibrations will be carried completely through thetransformer secondaries 15, but in view of the fact that the onlyconnection between the transformer primaries 11 and the transformersecondaries 12 is air, these vibrations will not be transmitted to thetransformer primaries.

With this first embodiment construction, therefore, the need for adirect flexible connection between the screen supporting frame 13, whichis vibrating, and a transformer unit, which is stationary, is completelyeliminated. By mounting-the transformer secondary 12 rigidly connectedto the screen supporting frame 13 for vibration with this screensupporting frame, and by providing merely an air connection between thetransformer secondary and the transformer primary 11, all possibility ofwear of the electrical connections for supplying electrical energythrough the screen cloths 18 is eliminated.

In the case of the second embodiment construction, where the flexiblecable 15 is positioned merely extending through the transformer primary11 but resting against the case thereof, there will be some slightfrictional wear between this cable 51.and the case'50, but under certainconditions this can be tolerated and the wear will still not approachthe wear incurred from a direct flexible cable connection as previouslyused with transformers of standard construction.

The most important broad'principle involved in the present invention isthe freedom of movement of the transformer secondary 12 relative to thetransformer primary- 11, so that the transformer secondary can besecured directly to the vibrating screen supporting frame 13with thetransformer primary being mounted stationary, and no excessive wear willtake place between vibrating and stationary members. Furthermore, in thefirst embodiment construction shown in FIGS. 1 through the entireconnection betweentransformerprimary 11 and transformer secondary 12 isair, so that here there can 1 be absolutely no wear.

It should be understood that in the first embodiment formof the presentinvention shown in FIGS. 1 through 6, wherein the connecting member 27of the transformer secondary 12 is supported by the side members 26;completely free of any contact with the transformer primary 11, thisconnecting member 27 could bea braided flexible cable such as indicatedat 51 in the second embodiment shown in FIG. 7, or could take on otherforms as conditions demand. Furthermore, in the preferred form thisconnecting member 27 can be solid for relatively low capacities andhollow with the possible addition of the holes 28 for higher capacitiesas conditions demand. I The important thing for higher capacities is tomaintain the temperature at a minimum in order to maintain voltage dropsto a minimum.

In the particular construction of vibrating screen unit 19 illustratedand described, merely the usual single phase electrical current is usedfor energizing the transformer primaries 11. This construction, however,is easily adaptable for the usual three-phase input current,-merely bythe provision of two transformer primaries 11 side by side with thesingle transformer secondary 12, and this will result in single phaseelectrical current being developed inthe transformer secondary 12.

Thus, according to the principles of the present invention, a broadmethod is provided of supplying electrical energy to a limited movableelectrical power consuming unit by providing a transformer primary 11with a transformer closed secondary circuit positioned extendinglongitudinally through the primary in such a manner that the secondaryis free of any physical connection with the primary which would restrictfree longi tudinal movement through the primary and free lateralmovement'within the primary. In the preferred form, the method wouldinclude providing only an air connection between the transformer primaryand transformer secondary.

In the foregoing description, certain terms have been used for brevity,clearness and understanding but no unnecessary limitations are to beimplied therefrom, be-

cause such words are used for descriptive purposes herein and areintended to be broadly construed.

Moreover, the embodiments of the improved. construction and methodillustrated and described herein are by way of example and the scope ofthe present invention is not. limited to the exact details ofconstruction shown.

Having now described the invention, the construction, operation and useof preferred embodiments thereof, and the advantageous new and usefulresults obtained thereby, the. new and useful construction and'methodand reasonable mechanical equivalents thereof obvious to those skilledin the art are set forth in the appended claims. t

I claim: 5 t

1. Electrically heated screen. construction including a transformerprimary having an opening formed therethrough, an electrically heatedscreen unit, spaced electrical connectors on the screen unitelectrically connected to a screen thereof and forming a closedelectrical circuit through said screen between said connectors, meansmounting the electrically heated screen unit for vibratorv movement,rigid'bar like transformer secondary means, means'suspending thesecondary means on the electrically heated screen unit, said secondarymeans extending through the transformer primary opening and withsecondary means ends connected and secured rigidly to the electricalconnectors of the screen unit for movement of; the secondary means withthe vibratory movement of the screen unit, the bar-like transformersecondarymeans being substantially hollow throughout the extent thereof,and the means suspending; the secondary means on the electrically heatedscreen unitpositioning said secondary means extending through theprimary openingfree of any physical contact with the primary.

2. Electrically. heated screen construction including a transformerprimary having an opening formed therethrough, an electrically heatedscreen unit, spaced electrical connectors on. the screen unitelectrically connected to a screen thereof and forming a closedelectrical circuit through said screen between said connectors, meansmounting the electrically heated screen unit for vibratory movement,rigid bar-lilie transformer secondary means, means suspending thesecondary means on the electrically heated screen unit extending throughthe transformer primary opening and with secondary means ends connectedand secured rigidly to the electrical con nectors of the screen unit formovement of the secondary means with the vibratory movement of thescreen unit, the bar-like transformer secondary means beingsubstantially hollow throughout the extent thereof and having a seriesof spaced holes formed therein opening into an interior thereof at leastin that portion of the secondary means extending through the primaryopening, and the means suspending the secondary means on theelectrically heated screen unit positioning said secondary meansextending through the primary opening free of any physical contact withthe primary.

3. Electrically heated screen construction including a transformerprimary having an opening formed therethrough, a vibrating electricallyheated screen unit having a main supporting frame mounted for vibration,selectively adjustable screen supporting means mounted on the supportingframe and selectively adjustable for positionin and tensioning a screenon the supporting frame, spaced electrical connectors rigidly secured tothe selectively adjustable screen supporting means movable with saidsupporting means in electrical connection with the screen and forming aclosed electrical circuit through the screen and between saidconnectors, rigid bar-like transformer secondary means, secondarysupport means rigidly suspending the transformer secondary means on thescreen unit supporting frame, said seconday means extending through thetransformer primary opening tor movement with the vibratory movement ofthe screen unit, the secondary means being a substantially hollow barthroughout tie extent ticreof and having ends, rigid selectivelyadjustable connection means between the secondary means ends and thescreen unit electrical connectors for selective movement between thescreen unit electrical connectors and secondary means, to allowselective adjustment of the screen supporting means during positioningand tensioning of the screen, and the secondary support means rigidlysuspending the secondary means on the screen unit supporting frameextending through the primary opening tree of any physical contact withthe primary.

Electrically heated screen construction including a transformer primaryhaving an opening formed therethrough, a vibrating electrically heatedscreen unit having a main supporting frame mounted for vibration,selectively adjustable screen supporting means mounted on the supportingframe and selectively adjustable for positioning and tensioning a screenon the supporting frame, spaced electrical connectors rigidly secured tothe selectively adjustable screen supporting means movable with saidsupporting means in electrical connection with the screen and forming aclosed electrical circuit through the screen and between saidconnectors, rigid bar-like transformer secondary means, secondarysupport means rigidly suspending the transformer secondary means on thescreen unit supporting frame, said secondary means extending through thetransformer primary opening for movement with the vibratory movement ofthe screen unit, the secondary means bein a substantially hollow barthroughout the extent thereof and having ends, the hollow secondanymeans having a series of spaced holes formed therein opening into theinterior thereof at least in that portion of the secondary meansextending through the transformer primary opening, rigid selectivelyadjustable connection means between the secondary means ends and thescreen unit electrical connectors for selective movement between thescreen unit electrical connectors and secondary means, to allowselective adjustment of the screen supporting means during positioningand tensioning of the screen, and the secondary support means rigidlysuspending the secondary means on the screen unit supporting frameextending through the primary opening free of any physical contact withthe primary.

5. in an electrically heated vibrating screen unit of the type in whicha screen is mounted adjustably tensioned on a main supporting frame ofthe screen unit and is resistance heated by passing electrical energytherethrough including vibrating means operabiy connected to the screenunit inducim substantially continuous vibratory movement or" the mainsupporting frame and screen during the electrical resistance heating ofsaid screen, selectively a justable screen supporting means mounted onthe main supporting frame engaged with said screen for vibrationdirectly with the main supporting frame and screen and selectivelyadjustable for positioning and tensioning the screen on the supportingframe, spaced electrical connectors secured rigidly with the selectivelyadjustable screen supporting means movable with said supp rting means inelectrical connection with the screen for vibration directly with thescreen and the passing of electrical energy through the screen toresistance heat said screen, a transformer secondary, secondary supportmeans rigidly suspending the transformer secondary on the mainsupporting frame, said secondary receiving vibratory motion from saidframe and vibrating directly with said frame and screen, the secondaryhaving ends, selectively adjustable rigid connection means between thesecondary ends and the electrical connectors for selective movementbetween the electrical connectors and secondary, to allow selectiveadjustment of the screen supporting means during positioning andtensioning of the screen, the secondary and connection means beingconstructed providing a closed electrical circuit through said secondaryand through said screen and back to said secondary, a transformerprimary having an opening formed therethrough, means mounting theprimary adjacent the screen unit and substantially free of the effect ofthe vibratory movement of the main supporting frame and screen, saidmeans mounting positioning the primary with the secondary extendingthrough said primary opening free of any physical contact between theprimary and secondary and free of the vibratory movement of thesecondary relative to the primary, and the primary being electricallyconnected to the secondary solely by air inducing electrical energy inthe secondary upon electrical energization of the primary.

5. Electrically heated screen construction as defined in claim 5 inwhich the transformer secondary is rigid and bar-like.

'7. Electrically heated screen construction as defined in claim 5 inwhich the transformer secondary is generally U-shaped, rigid andbar-like.

3. in an electrically heated vibrating screen unit of the type in whicha screen is mounted on the screen unit and is resistance heated bypassing electrical energy therethrough including vibratin means operablyconnected to the screen unit inducing substantially continuous vibratorymovement of the screen during the electrical resistance heating of saidscreen, said screen mounted on the screen unit for vibratory movement, atransformer secondary, rigid suspension means for connecting thetransformer secondary to the screen unit and receiving vibratory motionand through said rigid suspension means vibrating directly with saidscreen, means electrically connecting the transformer secondary to thescreen and providing an electrical circuit through said secondary andthrough said screen for the passing of electrical energy through saidscreen to resistance heat said screen, the transformer secondary havinga longitudinal portion extending spaced from the screen unit, atransformer primary having an l 1 opening formed therethrough, meansmounting the transformer primary adjacent to but spaced from the screenunit and substantially free of the effect of the vibratory movement ofsaid screenunit, the transformer primary being positioned withthesecondary spaced portion extending through the primary opening withthe primary substantially laterally surrounding the secondary spacedportion and being free of any physical connection with the secondarywhich would restrict free vibratory movement of the secondary relativeto the primary, and the primary being constructed electrically connectedto the secondary solely by said positioning inducing electrical energyin the secondary upon electrical energization of the primary.

9. Electrically heated screen construction as defined in claim 8 inwhich the transformer secondary spaced portion extends through theprimary opening free of any physical contact with the primary.

10. Electrical-1 y heated screen construction as defined in claim 3 inwhich the transformer secondary spaced portion extends through theprimary opening free of any physical contact with the primary; and inwhich the transformer secondary is rigid, bar-like and generallyU-shaped.

1 1. The method of supplying electrical energy to a substantiallycontinuously vibrating screen of an electrically heated screen unit toresistance heat the screen during said continuous vibration, includingthe steps of rigidly suspending a transformer secondary on the screenunit for vibration directly with the screen, electrically connecting thetransformer secondary with the screen forming an electrical circuitthrough the secondary and through the screen, positioning the secondaryextending with a portion spaced from the screen, positioning atransformer primary spaced from the screen and substantially free of theeffect of the vibratory movement of said screen, positioning the primaryrelative to the secondary substantially laterally surrounding thesecondary spaced portion for inducing electrical energy in saidsecondary upon electrical energization of said primary, and maintainingthe relative positioning of the primary and secondary totallyfree of anyphysical connection which would restrict free vibratory movement of thesecondary relative to the primary and which would transmit anyappreciable amount of the vibratory movement of the secondary totheprimary.

12. The method of supplying electrical energy to a substantiallycontinuously vibrating screen of an electri cally heated screen unit toresistance heat the screen during said continuous vibration, includingthe steps of rigidly suspending a transformer secondary on the screenunit for vibration directly with the screen, electrically connecting thetransformer secondary with the screen forming 1 an electrical circuitthrough the secondary and through the screen, positioning the secondaryextending with a portion spaced from the screen, positioning atransformer primary spaced from the screen and substantially free of theeffect of the vibratory movement of said screen, positioning the primaryrelative to the secondary substantially laterally surrounding andspacedfrom the secondaryspaced portion for inducing electrical energy insaid secondary upon electrical energization of said primary, andmaintaining the relative positioning of the primary and secondarysubstantially free of any physical contact between said primary andsecondary during the vibratory movement of the secondary. I

13; The method of supplying electrical energy to a substantiallycontinuously vibrating screen of an electrically heated screen unit toresistance heat the screen during said continuous vibration, includingthe steps of rigidly securing a generally U-shaped bar-like transformersecondary having spaced leg portions and a connecting portion on thescreen unit for vibration directly with the screen, electricallyconnecting the secondary leg portions with the screen forming a closedelectrical circuit through the secondary and through the screen,positioning the secondary with the secondary connecting portion spacedfrom the screen, positioning a transformer primary having an openingformed therethrough spaced from the screen and substantially free of theeffect of the vibratory movement of said screen, positioning the primaryrelative to the secondary'with the secondary connecting portionextending through the primary opening and spaced from the primary forinducing electrical energy in said secondary upon electricalenergization of said primary, and maintaining the relative positioningof the primary and secondary so that the primary and secondary aresubstantially totally free of any physicial contact during the vibratorymovement of the secondary.

14. The method of supplying electrical energy to a substantiallycontinuously vibrating screen supported on a vibrating main supportingframe of an electrically heated screen unit to resistance heat thescreen during said continuous vibration, including the steps ofsupporting a screen on the vibrating main supporting frame tensioned inoperable position with selectively adjustable screen supporting means ofsaid main supporting frame, rigidly suspending a bar-like transformersecondary having ends on the vibrating main supporting frame forvibration with the main supporting frame and screen, selectivelyadjustably and electrically connecting the secondary ends to theadjustable screen supporting means of the main supporting frame inelectrical contact with the screen supported by said screen supportingmeans forming a closed electrical circuit through the secondary andthrough the screen, positioning the secondary supported on the mainsupporting frame extending spaced from the screen, positioningatransformer primary having an opening formed therethrough spaced fromthe screen and substantially free of the effect of the vibratorymovement of said screen, positioning the primary relative to thesecondary with the secondary extending through the primary openingandspaced from the primary for inducing electrical energy in saidsecondary upon electrical energization of said primary, and maintainingthe relative positioning of the primary and secondary so that theprimary and secondary are substantially totally free of any physicalcontact during the vibratory movement of the secondary.

References fitted by the Examiner UNITED STATES PATENTS 743,331 11/03Ries. 962,828 6/10 Gin. 1,413,053 4/22 Onstad 219-221 1,515,593 11/24Elsdon-Dew 219-1049 1,626,295 4/27 Patschieder 219-50 1,733,250 10/29Davis 219-300 2,621,704 12/52 Langer. 2,703,392 3/55 Rex 338- 2,752,5786/56 Vt/inkel 338-130 2,850,163 9/58 Scanlonet a1. 209-238 2,868,3781/59 Burstlein 209-238 2,989,182 6/61 Burstlein 209-238 3,080,055 3/63Riesbeck 209-238 HARRY B. THORNTON Primary Examiner.

HERBERT L. MARTIN, MAX L. LE Y, Examiners.

11. THE METHOD OF SUPPLYING ELECTRICAL ENERGY TO A SUBSTANTIALLYCONTINUOUSLY VIBRATING SCREEN OF AN ELECTRICALLY HEATED SCREEN UNIT TORESISTANCE HEAT THE SCREEN DURING SAID CONTINUOUS VIBRATION, INCLUDINGTHE STEPS OF RIGIDLY SUSPENDING A TRANSFORMER SECONDARY ON THE SCEENUNIT FOR VIBRATION DIRECTLY WITH THE SCREEN, ELECTRICALLY CONNECTING THETRANSFORMER SECONDARY WITH THE SCREEN FORMING AN ELECTRICAL CIRCUITTHROUGH THE SECONDARY AND THROUGH THE SCREEN, POSITIONING THE SECONDARYEXTENDING WITH A PORTION SPACED FROM THE SCREEN, POSITIONING ATRANSFORMER PRIMARY SPACED FROM THE SCREEN AND SUBSTANTIALLY FREE OF THEEFFECT OF THE VIBRATORY MOVEMENT OF SAID SCREEN, POSITIONING THE PRIMARYRELATIVE TOTHE SECONDARY SUBSTANTIALLY LATERALLY SURROUNDING THESECONDARY SPACED PORTION FOR INDUCING ELECTRICAL ENERGY IN SAIDSECONDARY UPON ELECTRICAL ENERGIZATION OF SAID PRIMARY, AND MAINTAININGTHE RELATIVE POSITIONING OF THE PRIMARY AND SECONDARY TOTALLY FREE OFANY PHYSICAL CONNECTION WHICH WOULD RESTRICT FREE VIBRATORY MOVEMENT OFTHE SECONDARY RELATIVE TO THE PRIMARY AND WHICH WOULD TRANSMIT ANYAPPRECIABLE AMOUNT OF THE VIBRATORY MOVEMENT OF THE SECONDARY TO THEPRIMARY.